1. Field of the Invention
This invention relaters to concrete wedge anchors for construction and industrial applications.
2. Description of the Related Art
Concrete anchors are presently used in medium to heavy-duty construction and industrial applications to fasten machinery and equipment to masonry or concrete structures. Two general types of concrete anchors exist: Cast-in-place and retrofit. Cast-in-place anchors consist of a fastener cast within the concrete prior to curing, and retrofit anchors consist of a fastener installed after the concrete has sufficiently cured.
Three classes of retrofit anchors can be used: Bonded, undercut, and mechanical. A bonded anchor involves use of a type of bonding agent that bonds a fastener to the concrete, an undercut anchor consists of a specially shaped hole which allows a fastener to bear against, and a mechanical anchor consists of some sort of expansion mechanism that causes friction to support a load. All classes utilize a pre-drilled hole in the anchoring material.
Two different types of mechanical anchors are used in medium to heavy-duty applications: Torque controlled and displacement controlled. A torque controlled expansion anchor (typical expansion anchor) consists of wedging elements that are recessed within the anchor diameter. It is generally inserted with a nut and washer into a pre-drilled hole slightly larger than the anchor diameter until the nut and washer touch the concrete. Upon insertion, tightening of the anchor by rotating the nut clockwise draws the anchor away from the bottom of the hole. As the anchor draws up, the wedging elements engage into the sides of the concrete hole causing a wedging action , that supports an applied load. Typically, these expansion anchors have superior holding capacities over displacement controlled anchors and are easy to install, but they do not remain flush with the concrete and are very sensitive to hole diameter. If the diameter of the hole is too large or if the hole is out-of-round, the wedging element may not properly contact the sides of the concrete hole. Carbide drill bits commonly used in the industry for hole preparation commonly drill a hole that is out-of-round. The extent of this condition will determine the performance (holding value) of the anchor.
Another common problem with the typical expansion anchor is that when the anchor body is inserted into the hole, the presence of voids in the concrete at the point where the wedging element is to wedge against the side wall will require the anchor body to be withdrawn the distance of that void before the wedging element will get embedment in the side wall of the hole. This means the length of anchor body which protrudes from the hole will vary from hole to hole. Excessive bolt is often undesirable, which may require a portion to be cut off.
Displacement controlled anchors (typical drop-in anchors) consist of a cylindrical tube with an internal tapered expansion wedge cut longitudinally into sections at one end and female threads at the other A tapered expansion plug that matches, or closely matches, the taper of the internal expansion wedge fits inside the cylindrical tube. The anchor is generally inserted, threaded portion last, into a pre-drilled hole slightly larger than the anchor body until it is flush with, or slightly below, the level of the concrete and bears against the bottom of the pre-drilled hole. A setting tool is then used to drive the expansion plug into the expansion wedge that causes the sectional expansion wedges to expand into the sides of the concrete. Because the expansion plug must be driven into the expansion wedge, the anchor must bear against the bottom of the pre-drilled hole to support the anchor during setting. Another common problem is that since the anchor is often set overhead, the installer must wield an often heavy sledge overhead to install the anchor.
Once the anchor is set, a bolt or other threaded member is used to connect the threaded portion of the anchor to applied loads. Friction between the expanded wedges and the concrete hole supports these loads. Drop-in anchors remain flush with the surface of the concrete; but they are extremely difficult to install, hole depth dependent, and very expensive to produce.
Therefore, a need exists in the concrete anchor industry to produce a medium to heavy-duty mechanical anchor which is easy to install, is less sensitive to hole diameter,, is not hole depth dependent, has a known displacement on loading, is less sensitive to voids in,the concrete, has superior holding capacities, remains flush with (or below) the surface level of the concrete, and is less expensive to produce.